Recovery of calcium fluoride from fluorspar ore

ABSTRACT

Calcium fluoride is recovered from a finely mineralized fluorspar ore containing inclusions of barite within micron-size particles of fluorite. The ore is pugged and a fine-size fraction is recovered and roasted with a chloride salt, preferably calcium chloride, and carbon. The roasted product is lixiviated with water to remove the barium chloride reaction product and treated with hydrochloric acid to extract residual impurities. Alternatively, the roasted product is extracted directly with the acid. The acid-extracted product may be further purified by extraction with a hydrosulfurous compound.

United States Patent Mercade 51 Apr. 1 1972 54] RECOVERY OF CALCIUMFLUORIDE 2,985,508 5/1961 Fredrickson m1. ..23/90 x FROMFLUORSPAR ORE2,111,236 3/1938 Ball ..23/90 [72] lnventorz Venacio V. Mercade,Metuchen, NJ. FOREIGN PATENTS OR APPLICATIONS [73] Assignee: 'EngelhardMinerals & Chemicals Corpora- 208,705 1/19 68 U.S.S.R. ..23/90 tion,Township of Woodbridge, NJ. 1 11,753 5/1901 Great Britain ....23/88Filed: y 1970 138,486 2/1920 Great Britain "23/90 2 APPLNO; 33 PrimaryExaminer-Edward Stern I Attorney-Melvin C. Fhnt and Inez L. Moselle [52]U.S. Cl ..23/88, 23/90, 23/134, 57 ABSTRACT 23/312, 75/1, 75/2, 75/7 l51 int. Cl. ..c01r 11/22 Calcwm fluonde ls recovered from afinelvmmfirallzed fluor- 58] Field of Search 90 13 75/ 1 2 6 spar orecontaining inclusions of barite within micron-size par- 7 ticles offluorite. The ore is pugged and a fine-size fraction is recovered androasted with a chloride salt, preferably calcium chloride, and carbon.The roasted product is lixiviated with [56] References cued water toremove the barium chloride reaction product and UNITED STATES A ENTStreated with hydrochloric acid to extract residual impurities.Alternatively, the roasted product is extracted directly with 3,005,685l0/1961. Rled] et a] the acid. The acid-extracted product may be furtherpurified 292,742 7/1943 Beck by extraction with a hydrosulfurouscompound. 3,305,345 2/1967 Rausch et a1. 3,414,402 12/1968 Volk et a1...75/1 X 5 Claims, No Drawings BACKGROUND OF THE INVENTION Fluorsparores frequently contain appreciable quantities of barite (heavy spar) asan impurity. Calcium phosphate minerals, ferruginous matter andsiliceous impurities (e.g., clay) may also be present. Generally, someconcentration of the fluorite (calcium fluoride) from the barite iseffectedby hydraulic classification. Because barium sulfate is poorlysoluble or essentially insoluble in common reagents, the barite cannotbeextracted directly from the fluorite that is concentrated in fine-sizefractions of the ore.

Flotation has been widely used to remove barite from fluorite in certainores. A successful flotation concentration,

however, requires the physical liberation of the mineral parti- THE INVENTION An object of the invention is to provide a method forconcentrating fluorite in a finely mineralized ore containing baritegangue.

A specific object is to concentrate fluorite from barite in a mixturewhich does not respond to separation by flotation.

Another object is to provide a novel hydrometallurgicalpyrometallurgicaltechnique for recovering fluorite from a finely mineralized ore.

lhave found a simple, practical method for removing barite and otherimpurities from very finely mineralized fluorite ores of the typedescribed.

Stated briefly, the ore, preferably a fine-size fraction of the ore, isroasted in the presence of a chloride salt, preferably calcium chloride,and carbon, thereby converting the barium values into barium chlorideand sulfur values into acid-soluble form. The roasted product isextracted with hydrochloric acid solution, preferably after firstleaching'with water.

When the ore also contains ferruginous gangue, the roast may be deironedby magnetic purification prior to acid extrac tion and/or by means of ahydrosulfurous extraction after the extraction with hydrochloric acid.The hydrosulfurous reagent also removes residual phosphate values fromthe fluorite.

In a preferred embodiment of the invention, the ore is prepared bypugging it with water to promote the liberation of mineral values,blunging the pugged ore in water, fractionating the ore by hydraulicclassification, recovering a fine-size fraction and drying the fine-sizefraction. (All sizes in the micron-size range refer to values obtainedby the Casagrande sedimentation method.)

DETAILED DESCRIPTION After crushing, the ore is preferably mixed withwater and pugged in a suitable pug mill.

The ore is then pulped with water to prepare it for hydraulicclassification. A dispersing agent, e.g., a mixture of soda ash and acondensed phosphate salt such as tetrasodium pyrophosphate, ispreferably incorporated with the pulp. In most cases, coarse oreparticles should be removed from the pulp before carrying out afractionation step to recover a fine size fraction containingmicron-size particles. Removal of coarse particles may be accomplishedby passing the pulp through a screen having openings of a suitable size,e.g., a 325 mesh Tyler screen. Barite normally concentrates in the plus325 portion ofthe ore.

The pulp should be sufficiently dilute to permit fractionation at acut-off point which results in concentration of fluorite .in a fine-sizefraction. A well-dispersed 20 percent solids pulp is generally suitable.A fine-size fraction, typically percent minus 10 microns or finer,depending upon the particle size of the bulk of the fluorite particles,is recovered as an aqueous suspension. The fluorite concentrates inthefine-size fraction and barite concentrates in the coarse-sizefraction.

After fractionation, the resultinglow grade fluorite concentrate isdried and ground if necessary.

The low gradefluorite concentrate is mixed with a chloride salt andcarbon (unless the ore contains a significant amount of organicimpurity). The mixture, which may be pelletized if desired, is roastedat a temperature below the melting points of calcium fluoride and bariumsulfate. Temperatures of 760 C. and 1,100 C. have been usedsuccessfully. The roasting should be carried out under reducingconditions. A closed or partially closed roaster is employed.

The principal reaction involved when roasting the ore with calciumchloride and carbon is believed to be in accordance with the followingequation:

BaSO, CaCl 4C 9' BaCl CaS 4C0 Using chlorides other than calciumchloride, corresponding sulfidesare formed.

Chloride salts that may be used include monovalent and divalent chloridesalts, exemplified by chloride salts of sodium, potassium, lithium,ammonium, calcium, magnesium, strontium and barium. The cation of thechloride must be one which forms an acid-soluble sulfide. Calciumchloride is presently preferred for the reason that the added calciumrepresses ionization of calcium fluoride and thereby minimizes losses offluoride values during the subsequent acid extraction step. Sodiumchloride or a mixture of sodium chloride and calcium fluoride may bepreferred when the siliceous impurities are troublesome since the sodiumchloride may render such impurities soluble in the extracting solution.

It will be noted that barium chloride is soluble in water andhydrochloric acid of suitable concentration. Thus, this reaction productmay be removed by either reagent or a combination thereof. Calciumsulfide hydrolyzes in water and is soluble in. hydrochloric acid beforeand after hydrolysis.

Optimum proportions of carbon and chloride may be determined'by simpleexperimentation.

The chloride salts also supply chlorine which may attack clay matter andsome ferruginous impurities.

Fine ore tends to fonn aggregates during roasting. It is preferably topulverize the aggregates before treating the roasted product to purifythe fluorite.

If magnetic iron forms during roasting, it may be removed by wet or drymagnetic separation methods. This is preferably done prior to leachingwith acid. Wet-magnetic separation is preferable since barium chloridemay be removed from the roasted ore when the ore is pulped with water toprepare it for wet-magnetic purification.

The roasted, product may be lixiviated with water without a magneticpurification treatment in order to remove some or all of the bariumchloride.

As an alternative, the water-leaching step may be omitted and thehydrochloric acid extraction used to remove barium chloride as well asother impurities (e.g., calcium sulfide, aluminum and iron contained inclay gangue, iron coating the surfaces of the fluorite and bariteparticles, and calcium phosphate minerals such as apatite.)

Excellent results have been realized with dilute hydrochloric acid atelevated temperature.

It is possible to leach the residue obtained from the hydrochloric acidextraction with an alkaline leach using, for example, sodium carbonatesolution at elevated temperature, e.g., 180 F. The alkaline leachremoves silica.

The fluorite may be further purified by extraction with a hydrosulfurouscompound in acid media. This results in iron removal and, unexpectedly,it also removes considerable quantities of residual oxides ofphosphorous.

Features of the invention will be more fully understood and appreciatedfrom the following illustrative examples.

EXAMPLE The fluorite ore used in the test was mined in central Italy(Pianciano deposit). The fluorite in the ore was 93 percent by weightfiner than 3 microns. The minus 3 micron fluorite particles were highlycontaminated with minute inclusions of impurities, principally barite.Other fine impurities included clay, a phosphate mineral (apatite orfluorapatite), iron and calcium carbonate. Attempts to separate thefluorite and barite by froth flotation were unsuccessful. Prior to theData in Table I] show that by means of a chloridizing roast TABLE IIMetallurgical results-concentration of CaFz from finely mineralizedfluorspar ore by hydrometallurgy-pyrometallurgy Assays, wt, percentWeight, Products percent CuF- SiOz P105 B050:

(1) Minus 3 micron concentrate 100.0 78.0 1. 3 2. 58 5.0 (2) (1) Afterroasting and HCl1eaeh 71.1 90. 8 '1. 7 0. 92 0.1 (3) (2) After treatmentwith S02 and Na 104-. 67. 7 93. Z 0. -16 0. 1

V *=Yalues indicate that silica tray was attacked during roasting,

present invention, the highest grade products that were produced fromthe ore contained less than 80 percent CaF The ore was crushed to minus10 mesh and pugged with water at 65 percent solids for 2 hours. Thepugged ore was diluted with water to percent solids and the resultingore slurry was dispersed by adding soda ash in amount of 12 lbs/ton perton of solids in the slurry and 4 lbs/ton tetrasodium pyrophosphate. Thedispersed slurry was degritted by passing it through a 325 mesh (Tyler)screen. The minus 325 mesh dispersion was fractionated and a minus 3micron fraction was recovered for further processing.

The products were weighed and analyzed chemically. From these values,the distribution of minerals in the products were calculated. Resultsare summarized in Table I along with assays of the starting ore(heads").

Data in Table 1 show that a low grade fluorite concentrate (80.3 percentCaF )was obtained at a 92.9 percent recovery by pugging the ore,fractionating at minus 3 microns and recovering the minus 3 micronfraction. The low grade fluorite concentrate contained 78.8 percent byweight of the heads and was enriched in P 0 and silica as well as thedesired fluorite. The barium sulfate content of the low grade fluoriteconcentrate was 5.4 percent.

TAB LE I Iclaim:

1. A method for recovering calcium fluoride from an ore containingbarite gangue in which the bulk of the calcium fluoride particles arefiner than 10 microns and contain inclusions of impurities includingbarite which comprises:

pugging the ore,

forming the pugged ore into an aqueous pulp,

dispersing the pulp,

subjecting the dispersed pulp to fractionation,

recovering a fine size fluorite-enriched fraction of the pulp containingparticles substantially all of which are finer than 10 microns,

mixing the fine size fraction with sufficient calcium chloride andsufficient carbon to convert the barite to barium chloride roasting themixture at a temperature within the range of 760 to l,l00 C.,

lixiviating the roasted product with water,

and extracting the lixiviated product with hydrochloric acid.

2. The method of claim 1 including the step of extracting residualimpurities from the acid-extracted product with a hydrosulfurouscompound.

3. The method of claim 1 including the step of removing [Compositions offractions of pugged Italian fluorspar ore] Chemical analysis, wt.percent Distribution, wt. percent Weight, Products percent CaFz BaSOP205 S10; CflFz BaSO P205 810;

+325 mesh 8. 0 19. 3 54. 3 l. 5 4. 3 2. 3 27. 7 5. 3 17. 7 325 mesll+3uz13. 2 24. 8 54. 0 2. 1 2. 6 4. 8 45. 4 12. 1 17. 6 3p' 78. 8 80. 3 5. 42. 4 l. 6 92. 9 26. 9 82. 6 64. 7 Heads 100. 0 64. 0 18. 1 2. 1 2. 0100. 0 100. 0 100. 0 100. 0

'= 3# fraction also analyzed: 1.2% CaCO;; 0.08% Mn; 1.0% F9203.

The low grade fluorite concentrate was dried and given a chloridizingroast by mixing 100 g. of sample with 2.5 g. carbon and 5.7 g. CaClanhydrous and roasting the mixture in a silica tray for minutes at 1,093C. The tray was loosely covered with another silica tray duringroasting.

The roasted product was cooled to room temperature and diluted withwater. Concentrated hydrochloric acid (16 molar) was added in amount of14.0 g. The pulp at 15 percent solids was agitated for 60 minutes at 190F. The slurry was filtered, washed with water and dried.

The dried solids were slurried with water and sulfur dioxide was passedinto the slurry until the pH was 1.5. Sodium hydrosulfite (Na S O wasthen added in amount of 1.5 g. and the slurry was agitated for 10minutes. The slurry was filtered, washed and dried.

Analysis of the products at various stages of the process are summarizedin Table II.

iron from the roasted product by wet-magnetic treatment beforeextracting it with hydrochloric acid.

4. In a method for recovering calcium fluoride from finely dividedfluorspar ore containing barite in the gangue, the steps for removingthe barite from the ore which comprise: roasting said ore at atemperature within the range of 760 to l,100 C. in the presence of addedcarbon and a chloride salt which contains a cation which, during theroasting, forms a sulfide salt which is soluble in hydrochloric acid,said carbon and said chloride salt being added in amount sufficient toconvert said barite to barium chloride and an acid soluble sulfide,lixiviating the roasted ore with water and extracting the lixiviatedproduct with hydrochloric acid.

5. The method of claim 4 wherein said chloride salt is calcium chloride.

2. The method of claim 1 including the step of extracting residual impurities from the acid-extracted product with a hydrosulfurous compound.
 3. The method of claim 1 including the step of removing iron from the roasted product by wet-magnetic treatment before extracting it with hydrochloric acid.
 4. In a method for recovering calcium fluoride from finely divided fluorspar ore containing barite in the gangue, the steps for removing the barite from the ore which comprise: roasting said ore at a temperature within the range of 760* to 1,100* C. in the presence of added carbon and a chloride salt which contains a cation which, during the roasting, forms a sulfide salt which is soluble in hydrochloric acid, said carbon and said chloride salt being added in amount sufficient to convert said barite to barium chloride and an acid soluble sulfide, lixiviating the roasted ore with water and extracting the lixiviated product with hydrochloric acid.
 5. The method of claim 4 wherein said chloride salt is calcium chloride. 